Conventionally, corundum has been widely used as a filler in rubbers or plastics. For example, the corundum is used as a heat-radiating filler in a silicone resin, a silicone rubber or an epoxy resin. JP-A-H05-132576 and JP-A-2001-348488 disclose a resin composition using alumina particles and having excellent heat conductivity. JP-A-H11-209618 discloses a thermal conductive silicone gel composition containing alumina particles treated with a silane coupling agent. In the case of using the corundum as a heat-radiating filler, the heat-radiating performance is more enhanced by filling a larger amount of corundum in the resin, but an untreated corundum has poor affinity with the resin. The composition has, therefore, a high viscosity and may cause a molding failure when used for molding or an inhibition of curing when dispersed in a curable resin.
An object of the present invention is to obtain good affinity between a resin and corundum by surface-treating the corundum with a silicone compound and yield a kneaded product assured of a low viscosity, a uniform dispersibility and when a curable resin is used as the matrix resin, a high curing rate, so that the handling and moldability of the resin composition can be enhanced.